Hearing loss is one of the most common birth defects and can be caused by a malformation of the inner ear. Understanding the normal development of the inner ear can be used to further understand the causes of such defects and ultimately correct them. The objective of this proposal is to investigate the mechanisms involved in the first stage of inner ear development - the formation of the otic placode, a simple patch of ectoderm from which the whole inner ear originates. Previous studies have shown that FGF signaling played a critical role in otic placode formation. However, several studies, including data from our laboratory, have suggested the existence of a second FGF-independent pathway. Our preliminary data identified BMP4 as a good candidate for otic placode induction. It is indeed expressed at the right location - the neural fold adjacent to the future otic placode - at the right time and it is sufficient to induce at least two ear specific markers, BMP7 and Dlx3 in competent tissue. Thus, we hypothesize that BMP4 is implicated in the FGF-independent induction of some otic placode markers. We propose to test this hypothesis in the following specific aims: 1. To determine whether the neural fold , but not the cranial mesoderm, is necessary for induction of FGF independent otic markers. We will surgically ablate these tissue in chick embryos. 2. To determine the sufficiency of the neural fold to induce otic markers in competent ectoderm. We will combine and culture responding ectoderm to neural fold and analyse the expression of otic markers. 3. To test the necessity of BMP4 signaling. We will culture head chunks comprising the otic ectoderm with inhibitors of the BMP signaling pathway. 4. To assess the sufficiency of BMP4 signaling. We will culture competent ectoderm in presence of BMP4 and analyse the expression of a variety of otic markers. This project studies the earliest events of inner ear development. The information it will provide will represent a major step in understanding the molecular mechanisms underlying the formation of the inner ear.